1. Field of the Invention
This invention concerns a complete lighting unit, also called aluminaire, that combines a natural daylighting source for white light formed by luminescent solar concentrators and an artificial source having an automatic dimming/brightening capability in response to the presence of daylight.
2. Description of the Prior Art
The use of daylight for interior building illumination has in recent years been explored by innovators in lighting design and technology. A variety of concepts are being pursued that show some promise for introducing reasonable levels of daylight into a building for general illumination.
Many of the collector designs are based on configurations that require mechanical tracking of the sun by heliostats or rotating Fresnel lenses, for example. Still other concepts that do not require tracking have been described. These concepts include: diffractive optics, i.e. holographic optical elements; and reflective cylinders. The obvious advantage of nontracking collectors over those that must track the sun is the elimination of moving parts. In either case, however, the principal function is the collection of direct solar rays and this process requires, in almost all cases, focusing on the sun itself. Some examples of recently known prior art lighting systems follow.
U.S. Pat. No. 4,039,816, issued to Gareis in 1977, discloses an arrangement for transmitting light energy from a light source through a stack of light-conducting members. Each member collects a different portion of the light energy illuminated from the light source and guides its portion along a prescribed path to its reflecting surface which then reflects the light energy through a Fresnel lens.
U.S. Pat. No. 4,152,752, issued to Niemi in 1979, discloses an illumination system for a building in which light pipes distribute light from both artificial and natural light sources. Sunlight is received directly by a conventional stationary solar collector/concentrator and is directed by light pipes to light fixtures. An artificial light source is disposed within a housing having a suitable reflector, such as a parabolic type, for directing high intensity light through the light pipe to a splitter which combines it with light from the natural source. The artificial light source may be a high intensity lamp, such as a mercury vapor lamp or the like. A dimmer switch is also provided for the light fixture.
U.S. Pat. No. 4,411,490, issued to Daniel in 1983, shows an apparatus for collecting solar radiation as a single beam through a lens system which provides a coherent light beam to a light pipe. The distribution system may employ a Fresnel lens as the light fixture which is mounted in a ceiling panel of the building.
U.S. Pat. No. 4,422,719, issued to Orcutt in 1983, discloses a light distribution system including a light guide having a square cross section.
U.S. Pat. No. 4,428,031, issued to Mori in 1984, discloses an illumination device for directing sunlight into the interior of a room after passing through a Fresnel lens. The light source is the sun and the rays emanating from the sun are carried by an optical wave guide which may be a bundle of optical fibers.
Thus, it may be seen that, in the known prior art devices, there is not a system combining luminescent solar concentrators (LSC) and an artificial source having an automatic dimmer/brightener responsive to a daylight sensor.
U.S. Pat. No. 4,329,535, issued to Rapp in 1982, discloses a thin film LSC capable of efficiently concentrating both the diffuse and direct components of sunlight at all angles of incidence while remaining completely stationary. The only known prior use of such LSC has related to their use in photovoltaic cells.
U.S. Pat. No. 4,260,220, issued to Whitehead in 1981, discloses a prism light guide that may serve as a distributor for efficiently propagating light. However, the nature of the light sources used with the distributive light guide is not disclosed.
Therefore, for all practical purposes, there is not a highly efficient lighting system for bringing daylight deep within the interior of a building because, presently, interior daylighting is substantially restricted to the perimeter and near perimeter locations, i.e. space situated close to apertures, such as windows and skylights, in buildings.